No you do not.
No. It is free to play.
you need it to install it
You just need to buy the game. There is no online fee. It is free to play. Diablo 3 is free to play. There are no monthly fees unless you decide to use the RMAH.
the original game and a working computer.
you need expansion set and then you kill diablo talk to tyreal the archangel a portal will apperar go in it
Diablo 3 needs a constant internet connection if you want to play it, so yes it does need WiFi if that is what you use to connect to the internet. Hope this helps.
yeah man diablo 2 is a totally different game than diablo 1
Windows Vista can play Diablo 2 with no problems at all. Just install it normally and double click it and play, no harder than that.
Yes, of course people play Diablo 2: Lord of Destruction. And most people probably will until the release of Diablo 3. And even then, people probably might still play it from time to time.
After you buy it from a store, it is free to play after that.
You can not.
You might be able to find it on a digital store, like Good Old Games. On a digital download, there'll be no need for play disks.